One afternoon last week, Public Advocate Bill de Blasio held a hearing 15 floors up in the Municipal Building on the subject of skyrocketing (and often inaccurate) water bills. The session was crowded with reporters and regular New Yorkers waving copies of their water bills. It was a unique occasion, marking the first time that any public advocate had convened a public hearing. At issue was the most mundane stuff of government, filled with charts, accusations of tin-eared bureaucrats and discussions over how to reform obscure oversight agencies.

It also marked a significant shift in the 2013 race for mayor.

For as much as the powwow allowed homeowners to gripe about the Department of Environmental Protection, the hearing was really aimed at small business owners, who often get stuck with the bill when rates skyrocket. Combine that with what Mr. de Blasio’s aides called a “major speech” to the city’s grandees about fostering economic growth at NYU the week prior, and a new focus by Mr. de Blasio on the city’s accelerating use of fines on restaurants and small business owners—including a lawsuit to determine exactly how much the city government has been relying on revenue from fines—and it adds up to a picture of a top contender to be the city’s next mayor making a concerted pitch to the city’s business community.

Mr. de Blasio is in many ways an unlikely person to be making that pitch. He vaulted into his current job—the second highest ranking spot in city government—based on his close ties with labor unions, and with the left-leaning Working Families Party in particular. Formerly an aide to both David Dinkins and Hillary Clinton, he has never really worked in the private sector. When he criticized the NYPD’s stop-and-frisk policy recently, a mayoral spokesman all but accused him of trying to put the ACLU in charge of the police department.

But with the election now less than a year away, campaign coffers need to be filled and key constituents courted.

In a recent phone interview, Mr. de Blasio disputed the notion that he was tacking to the center.

“To me, it is trying to express as public advocate where we need to go and how do we address some of the challenges we face and how I feel on a range of issues and how they connect. When you see the dots connect, it is clear there is no contradiction. Maybe certain people focus more on one part of the work I was doing and ignore the other parts,” he said. “I am a serious public servant. I have been at this work a long time. For this city to succeed, what we need to do right now is balance the interests of the business community and labor.”

Mr. de Blasio’s newfound focus does seem like an effort to avoid a caricature of him as a Cesar Chavez clone in City Hall just as voters begin to tune into the race.

“It is the Ronald Reagan debate question: ‘Are you better off than you were four years ago?’” he explained. “The Bloomberg equivalent is an easier environment for business than it was 10 years ago. Is it easier for business to navigate the city government than it was 10 years ago? A lot of people in the business world will say no, it is actually harder. A lot of people in the development world will say no, it is actually harder.”

When it was pointed out to Mr. de Blasio that it was somewhat jarring to hear him approvingly quote Ronald Reagan, he trotted out a few more.

“Morning in America! I’ve got a million of them. There you go again, David! There you go again.”